Cause:
A Fan Booster Switch has been added to the AR4018A, AR4018IA, AR4024A, AR4024IA, AR4038A and AR4038IA.

Resolution:
The fan booster switch was added to the NetShelter CX cabinets to increase airflow, but the Owner's Manual has not been updated yet.
For more information regarding this switch please see the attached file.